Website on Darkweb

First you don't need to call it the "dark web" its the same web everyone uses just not filtered and restricted. if you are simply trying to run a .onion address you can do this onion hosting service providers.
maximum security? the language depends on what your doing with said site. html/css is the norm and is fine if its written properly. secure it with a htaccess file but ultimaly if someone wnats to get in and you leave any hole they can.
if you are going to host something someone wants then you need to hire someone who sole job in web security.